Subarachnoid space: new tricks by an old dog

Abstract

Purpose: The purpose of the study was to: (1) evaluate the subarachnoid space (SAS) width and pial artery pulsation in both hemispheres, and (2) directly compare magnetic resonance imaging (MRI) to near-infrared transillumination/backscattering sounding (NIR-T/BSS) measurements of SAS width changes in healthy volunteers.

Methods: The study was performed on three separate groups of volunteers, consisting in total of 62 subjects (33 women and 29 men) aged from 16 to 39 years. SAS width was assessed by MRI and NIR-T/BSS, and pial artery pulsation by NIR-T/BSS.

Results: In NIR-T/BSS, the right frontal SAS was 9.1% wider than the left (p<0.01). The SAS was wider in men (p<0.01), while the pial artery pulsation was higher in women (p<0.01). Correlation and regression analysis of SAS width changes between the back- and abdominal-lying positions measured with MRI and NIRT-B/SS demonstrated high interdependence between both methods (r = 0.81, p<0.001).

Conclusions: NIR-T/BSS and MRI were comparable and gave equivalent modalities for the SAS width change measurements. The SAS width and pial artery pulsation results obtained with NIR-T/BSS are consistent with the MRI data in the literature related to sexual dimorphism and morphological asymmetries between the hemispheres. NIR-T/BSS is a potentially cheap and easy-to-use method for early screening in patients with brain tumours, increased intracranial pressures and other abnormalities. Further studies in patients with intracranial pathologies are warranted.

Figure 1. Dots and whisker plots show the mean left frontal (blue), right frontal (green), left occipital (red) and right occipital (purple) SAS width measured with MRI in females (n = 9) and males (n = 6).

The dots represent the means and the whiskers the 95% confidence intervals. Statistical significance (p values or NS for not statistically significant) are for sex asymmetries (females vs. males).

Figure 2. Dots and whisker plots show the mean left (blue) and right (green) frontal SAS width (sas-TQ) in the sitting position, and left (red) and right (purple) frontal SAS width (sas-TQ) during the BOPT measured with NIR-T/BSS in females (n = 23) and males (n = 15).

The dots represent the means and the whiskers the 95% confidence intervals. Statistical significance (p values or NS for not statistically significant) are for sex asymmetries (females vs. males).

Figure 3. Dots and whisker plots show the mean left (blue) and right (green) pial artery pulsation (cc-TQ) in the sitting position, and left (red) and right (purple) pial artery pulsation (cc-TQ) during the BOPT measured with NIR-T/BSS in females (n = 23) and males (n = 15).

The dots represent the means and the whiskers the 95% confidence intervals. Statistical significance (p values or NS for not statistically significant) are for sex asymmetries (females vs. males).

Figure 4. Histogram of percentage changes in results by switching from a lying-back position to an abdominal-lying position using the MRI method.

Figure 5. Histogram of percentage changes in results by switching from a lying-back position to an abdominal-lying position using the NIR-T/BSS method.

Figure 6. Histogram of percentage changes in results by switching from a lying-back position to an abdominal-lying position using both methods.

Figure 7. Histogram of differences between the percentage changes for MRI and NIR-T/BSS methods.

Figure 8. The mean value of percentage changes in results by switching from a lying-back to an abdominal-lying position using both methods.

Figure 9. The standard deviation of percentage changes in results when switching from a lying-back position to an abdominal-lying position using both methods.

Figure 10. Correlation diagram of changes in results when switching from a lying-back position to an abdominal-lying position using both methods.

Figure 11. An NIR-T/BSS tracing demonstrating the sas-TQ change between the back- and abdominal-lying positions.

The first marker indicates the change from the back- to the abdominal-lying position, while the second marker indicates the change from the abdominal- to the back-lying position.